Complexation of anionic conjugated polyelectrolyte with cationic surfactant

Abstract

In recent years, conjugated polymers have been a target of intensive investigation for application in a variety of areas such as light-emitting diodes, organic transistors, and sensors etc. In particular, water-soluble conjugated polyelectrolytes have been widely recognized as biological and chemical sensors for specific targets such as ions, proteins, and nucleic acids. Several studies have shown that the fluorescence of conjugated polyelectrolytes can be efficiently quenched by ionic species such as methyl viologen (MV) with extremely high sensitivity. The Stern-Volmer constants (KSV) for MV quenching of poly(2,5-methoxyproplyoxy sulfonate phenylene vinylene) (MPS-PPV) and sulfonated poly(phenylene ethynylene) (PPE-SO3) in water range from 10 to 10 M. The mechanism for the efficient quenching was proposed to be due to a combination of efficient exciton migration within the polymer chain and a rapid charge transfer quenching between the polymer and MV. The efficient fluorescence quenching of conjugated polyelectrolytes provides a basis for a new class of sensitive biological and chemical sensors. Chen et al. demonstrated that optical and chemical properties of the polymer can be controlled by combining the anionic conjugated polyelectrolyte, MPS-PPV, with a cationic surfactant dodecyltrimethyl-ammonium bromide (DTA). They showed, by studying the quenching behavior of MV, that the conjugated polymer associated with the surfactant has different geometric conformation from that of the free polymer, which can hinder the self-aggregation of the polymer chain in water. In this work, based on the fluorescence quenching study, we report on the complexation characteristics of the anionic conjugated polyelectrolyte, PPE-SO3, with the cationic surfactant, tetraoctylammonium bromide (TOAB).